1. Field of the Invention
The present invention relates to a color electro-photographic apparatus, and more particularly to a desk-top type small size laser printer.
2. Description of the Prior Art
In the prior art concerning the apparatus, as described in, for example, Japanese Patent Application Laid-Open No. 3-106736 (1991) and Japanese Utility Model Application Laid-Open No. 3-77941 (1991), photosensitive drums for four colors are individually placed in a single line in the lateral direction, an endless intermediate transfer belt being provided such as to touch with the bottom parts of the photosensitive drums.
In the apparatus described above, driving of the photosensitive drums and the intermediate transfer belt is performed by driving all of the photosensitive drums and the intermediate transfer belt using a single drive unit or by driving them individually using independent drive units.
Developing means for four colors are placed in a rank under a single photosensitive member being endless-belt-shaped to superpose four color toner images on the photosensitive member, as described in Japanese Patent Application Laid-Open No. 4-326373 (1992).
In the apparatus described in Japanese Patent Application cartridge as to be easily mounted and dismounted by the users.
On the other hand, in the color electro-photographic apparatus where developing means for four colors are individually placed in a single line in the lateral direction, an endless-belt-shaped photosensitive member being touched with an intermediate transfer member on a cylinder, a color image being obtained by means of superposing each of color images on the transfer member; the accuracy in color adjustment is required to be approximately below 100 .mu.m, and in order to realize this accuracy the average accuracy is required to be below 60 .mu.m.
It has not been realized the apparatus in which the market needs such a usability is compatible with the basic specification of color electro-photography.
In order to realize a disk-top small sized color laser printer, it is desirable for small size and low cost to realize a so called one motor type apparatus in which a transfer member on a cylinder is driven by an endless-belt-shaped photosensitive member. However, there are disadvantages that there appears the displacement in colors due to the difference between the thermal expansion of the drive pulley rotating the photosensitive member and the thermal expansion of the transfer member, the displacement in colors by the change in transferring speed ratio from the photosensitive member to the transfer member due to change in the thickness of toner layer or the effect of toner overlaying caused by developing condition change due to deterioration with age or change in temperature.
Objects of the present invention are to solve the problems described above, and to provide a color electro-photographic apparatus which is small in size and light in weight, being capable of performing its maintenance by a user himself, producing a high quality picture by means of highly accurate color adjustment.
In order to attain the above objects, the construction to realize a high quality picture by means of superposing once each color of toner images on an intermediate transfer member is constructed such that developing means for four colors are placed in a rank above a single endless-belt-shaped photosensitive member, each color of toner images on the photosensitive member is touched with a photosensitive member formed in an approximately oval on its major axis side to transfer the image.
In addition to this, the photosensitive member is employed a cartridge type for easiness of user's maintenance and for capability of highly accurate positioning between the body of apparatus and the photosensitive member cartridge when a user changes the photosensitive member.
The following are embodiments of a color electro-photographic apparatus according to the present invention.
A color electro-photographic apparatus having a photosensitive member for forming an electro-static latent images on it by exposure, a plurality of developing means for forming toner images from the electro-static latent images formed on the photosensitive member by exposure, a transfer member for transferring the toner images on it, wherein the photosensitive member is endless-belt-shaped, the transfer member being drum-shaped. And a plurality of the developing means are placed in a single rank.
Further, a color electro-photographic apparatus having an endless-belt-shaped photosensitive member for forming an electro-static latent images on it by exposure, developing means for forming toner images from the electro-static latent images formed on the photosensitive member, a transfer member for transferring the toner images on it by touching with a part of the photosensitive member, wherein a plurality of the developing means are placed in a single rank, the endless-belt-shaped photosensitive member being laterally stretched to form approximately an oval shape such as to touch with each of the developing means, the endless belt and the transfer member being placed laterally such that the edge surface in the major axis side of the endless belt touches with the transfer member.